It was said (ερρεθη). First aorist passive indicative of ειπον.

That they should not hurt (ινα μη αδικησουσιν). Sub-final (object clause subject of ερρεθη) with ινα μη and the future active of αδικεω as in Revelation 3:9; Revelation 8:3. Vegetation had been hurt sufficiently by the hail (Revelation 8:7).

But only such men as (ε μη τους ανθρωπους οιτινες). "Except (elliptical use of ε μη, if not, unless) the men who (the very ones who)." For this use of οστις see Revelation 1:7; Revelation 2:24; Revelation 20:4.

The seal of God upon their foreheads (την σφραγιδα του θεου επ των μετωπων). Provided for in Revelation 7:3. "As Israel in Egypt escaped the plagues which punished their neighbours, so the new Israel is exempted from the attack of the locusts of the Abyss" (Swete).